System and method for dual energy and/or contrast enhanced breast imaging for screening, diagnosis and biopsy

ABSTRACT

Systems and methods for x-ray imaging a patient&#39;s breast in combinations of dual-energy, single-energy, mammography and tomosynthesis modes that facilitate screening for and diagnosis of breast abnormalities, particularly breast abnormalities characterized by abnormal vascularity.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation of pending U.S. patent applicationSer. No. 13/415,675, filed Mar. 8, 2012, which claims priority under 35U.S.C. § 119 from provisional U.S. Patent Application Ser. No.61/450,304 filed Mar. 8, 2011, the contents of which are incorporatedherein by reference.

FIELD

This patent specification relates to medical imaging and morespecifically to a system that enables selection among a plurality ofdifferent imaging modes, a plurality of different imaging processes,image acquisition parameters and image processing techniques.

BACKGROUND

Several references are listed at the end of the disclosure portions ofthis patent specification and are referred to below by numbers inparenthesis. These references a well as prior patents identified in thispatent specification are hereby incorporated by reference.

In the U.S. breast cancer mortality is second only to that of lungcancer for women. Because of its role in early tumor detection, x-raymammography has become them most commonly used tool for breast cancerscreening, diagnosis and evaluation in the United States. A mammogram isan x-ray image of inner breast tissue that is used to visualize normaland abnormal structures within the breasts. Mammograms provide earlycancer detection because they can often show breast lumps and/orcalcifications before they are manually palpable.

While screening x-ray mammography is recognized as the most effectivemethod for early detection of breast cancer, it also presents challengesin that in some cases it may be difficult to determine whether adetected abnormality is associated with a cancerous or benign lesion.One reason for this is that a mammogram Mp is a two dimensionalprojection image representing a three dimensional structure, andoverlapping structures in the compressed breast may confound imageinterpretation and diagnosis. A second reason is that the x-rays thatare often used to obtain the images have energies that are in a rangethat helps achieve a desirable Signal to Noise Ratio (SNR) but at thesame time may cause the x-rays to be attenuated to a similar degree bybreast structures that may have different clinical significance.

Efforts to improve the sensitivity and specificity of breast x-rays haveincluded the development of breast tomosynthesis systems. Breasttomosynthesis is a three-dimensional imaging technology that involvesacquiring images of a stationary compressed breast at multiple anglesduring a short scan. The individual projection tomosynthesis images Tptaken at respective angles of the imaging x-ray beam relative to thebreast are then computer-processed into a series of reconstructedtomosinthesis slice images Tr each representing a respective slice ofthe breast. The Tp and/or Tr images can be displayed individually orconcurrently or in a dynamic cine mode. Breast tomosynthesis mammography[see references 14-19] typically uses a field digital mammography (FFDM)platform. In one example, an x-ray tube moves in an arc above the breastand a series of 11 to 22 low dose x-ray 2-D tomosynthesis projectionimages Tp is obtained. The sum of the dose from all of the 2-Dtomosynthesis projection images Tp is similar to the dose from a singleconventional digital mammogram Mp. These low-dose 2-D tomosynthesisprojection images Tp are reconstructed into a series of 3-D slice imagesTr each representing a slice of the breast where each slice is, forexample, 1-5 mm thick. The slice images typically conform to planesparallel to the platform supporting the breast during image acquisition,but could be oriented differently. An advantage of breast tomosynthesiscompared to conventional mammography is that by showing the breast as aseries of slices rather than a single mammogram, a lesion may be seenwith greater clarity because much of the superimposed tissue present ina conventional mammogram has been removed.

Reconstructed tomosynthesis slice images Tr reduce or eliminate problemscaused by tissue overlap and structure noise in two-dimensionalmammography imaging. Digital breast tomosynthesis also offers thepossibility of reduced breast compression, improved diagnostic andscreening accuracy, fewer recalls, and 3D lesion localization. Anexample of a multi-mode breast tomosynthesis/mammography system isdescribed in commonly assigned U.S. Pat. No. 7,869,563. Other aspects ofbreast tomosynthesis and mammography are described in commonly assignedU.S. Pat. Nos. 7,991,106, 7,760,924, 7,702,142, and 7,245,694, which arehereby incorporated by reference.

In an effort to address challenges in differentiating breast cancer frombenign abnormalities in breast x-ray imaging, consideration has beengiven to contrast-enhanced and dual-energy imaging. In contrast-enhancedimaging, a contrast agent that may be iodine-based is introduced intothe breast, typically through an injection in a vein remote from thebreast, and x-ray images are taken after (as well as possibly before)the contrast agent has reached the breast. The contrast agent helpshighlight vascularity in the breast. If images of the same breast takenbefore and after the arrival of the contrast agent in the breast aresubtracted from each other (and absent breast motion between the timesthe two images are taken), breast vascularity may be appear even moreclearly in the resulting subtraction image. This may assist indifferentiating cancer from benign tissue because it is believed thatbreast cancers release angiogenesis factors that increase the formationof small vessels near the tumor (1, 2). (The Arabic numbers inparenthesis refer to respective publications listed at the end of thispatent specification.) It is believed that the growth of breast canceris dependent on angiogenesis, and that these vessels differ from normalvessels in that they have increased permeability and are often tortuous.Imaging of the vessels around a tumor is believed to allow improveddetection of breast cancer.

MRI (Magnetic Resonance Imaging) can be used with contrast enhancementto help characterize breast cancers by imaging the vascular network neara breast cancer (3). Although contrast enhanced breast MRI (CEMRI) canbe effective in imaging breast cancer it has limitations including highcost, long procedure time, enhancement of benign abnormalities such asfibroadenomas, and inability to image women with metal clips orclaustrophobia. Typically, the contrast agent used in CEMRI isgadolinium-based and is different from the contrast agents used in x-rayimaging.

X-ray imaging also can use contrast enhancement to improve cancerdetection. The use of contrast agents such as iodine with x-ray methodshas been suggested for imaging the vascular network near a breastcancer. These x-ray imaging methods include breast CT (4, 5), breasttomosynthesis (6, 7) and digital mammography (8-13). Contrast enhancedx-ray mammography (CEM) may improve the conspicuity of breast cancers(8-13). It has also been suggested that CEM may provide improvedspecificity compared to CEMRI because fewer benign lesions enhance (13).These studies are small and may need to be validated with larger trials.

In x-ray mammography, contrast enhanced mammography has been evaluatedusing two methods. The first involves subtraction of images obtainedpre- and post-contrast (9). This method is referred to as timesubtraction. The second method is referred to as dual-energy contrastimaging. In this method images are obtained at low energy and highenergy after the injection of contrast. The images are obtained atenergies above and below the k-edge of iodine (33.2 keV) wheniodine-based contrast agent is used. At x-ray energies just above thek-edge the absorption of x-rays is increased resulting in an increase ofcontrast from the iodine contrast agent in the high energy image.Subtraction of these two images enhances iodine contrast whilesuppressing the contrast of normal breast anatomy. An advantage ofdual-energy contrast imaging mammography is that both images may beobtained in a very short time and therefore the images may be subtractedwith little patient motion. This is not true for subtraction of pre- andpost-contrast images since typically there will be more than a minuteseparating the acquisition of the two images.

One goal of any x-ray imaging system is to obtain the highest qualityimages to reduce the occurrence of false positive and false negativediagnoses. It would be desirable to identify a system and method foracquiring x-ray images to alleviate issues associated with specificityand sensitivity in current designs.

SUMMARY OF THE DISCLOSURE

The patent specification describes x-ray imaging systems and methodsthat facilitate x-ray screening and diagnosis of patients, particularlyof patients' breasts, and particularly for abnormalities characterizedby suspicious vascularity. In a non-limiting example, combination ofimaging modes are used, preferably in a single breast compression, toobtain a collection of x-ray images that provide unexpectedly betterfacility of screening and diagnosis of such abnormalities. As oneexample, the new system and method are used to image a patient's breastafter an x-ray contrast agent has been introduced in the breast. Aselected time after injecting the contrast agent, the system obtains 3Dslice images representing respective slices of a patient's breast. These3D slice images are formed by computer-processing, through areconstruction algorithm, a multiplicity of x-ray 2D tomosynthesisprojection images of the breast taken at respective angles of an imagingx-ray beam to the breast. The system also obtains a 2D combination imageof a low-energy 2D x-ray mammogram and a high-energy 2D x-ray mammogramof the breast. These 21) projection images and low-energy and hig-energymammograms preferably are obtained in a single compression of thepatient's breast. The system displays, preferably concurrently, the 2Dcombination image and one or more of the 3D slice images. The displayedcombination 2D image facilitates identification of a position of apossible vascular abnormality in two dimensions, and the 3D slice imagesfacilitate identification of the position of the abnormality in threedimensions and enables visualization of the appearance of theabnormality in respective slice images.

These and other aspects of the system and method are further explainedin the detailed description that follows and in the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an x-ray breast imaging system that provides a choiceof multiple imaging modes including a 3D tomosynthesis mode and a 2Dmammography mode, in each case using single-energy imaging ofdual-energy imaging, and in each case with or without a contrast agentin the breast.

FIG. 2 illustrates in greater detail a portion of the FIG. 1 system.

FIG. 3 illustrates further aspects of the FIG. 1 system.

FIG. 3 a illustrates an example of a variable filter/collimatormechanism.

FIG. 4 illustrates steps in an example of operation of a breast imagingsystem.

FIG. 5 illustrates a customization table for parameters used in carryingout breast imaging.

FIG. 6 a illustrated a display of images taken in different aging modesof a system such as that illustrated in FIG. 2 ,

FIG. 6 b schematically illustrates a display of ages taken in sixdifferent imaging modes of a system such as that of FIG. 1 .

FIG. 7 illustrates possible combinations of imaging modes of a systemsuch as illustrated in FIG. 1 .

FIG. 8 is a similar illustration of possible combinations of imagingmodes in a system that takes only 2D images.

FIG. 9 is a similar illustration of possible combinations of imagingmodes in a system that takes only 3D images.

FIG. 10 illustrates steps in a preferred example of operation of asystem such as illustrated in FIG. 1 .

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The examples of systems and methods described in this patentspecification leverage and combine advantages of one or more imageacquisition modes, including two-dimensional (2D), three-dimensional(3D), dual-energy (DE) and contrast-enhancement (CE) imaging to providea breast imaging system with improved sensitivity and specificity andwith benefits for more efficacious screening and diagnosis, greaterconvenience for the radiologist and better patient workflow.

A system according to one example includes an x-ray source including oneor more x-ray filters, an imaging x-ray detector, and an immobilizationmechanism positioned between the x-ray source and the detector forimmobilizing an object to be imaged such as a patient's breast. Duringimage acquisition, X-rays of two or more different energy ranges aregenerated from the x-ray source by varying at least one x-ray sourceacquisition parameter, including but not limited to the x-ray filtersand x-ray kV. The x-rays prop to through the imaged object and arereceived by the detector. The composition of the imaged object modulatesthe x-rays through mechanisms such as attenuation, absorption andscatter, resulting in relatively brighter and darker areas in a detectedimage. The detected image is processed using computer-processingtechniques and the resulting images may be stored and/or displayed at aradiologist's workstation.

The system may include a control module for controlling imageacquisition, the control module including a user interface permitting auser to select one or more modes of image acquisition and/or imageprocessing. The user interface may comprise a key pad, touch pad,joystick or other input mechanism that interacts with a computer programexecuting on a computer system coupled to a display. Such a userinterface may enable selection of image acquisition mode, such as a 2Dmammography mode, a 3D tomosynthesis imaging mode or a combination 2D/3Dimaging mode depending upon the capabilities of the breast imagingdevice.

Alternatively (or in combination) the interface may enable furthercustomization of image acquisition via selection of particularacquisition parameters and acquisition processes within each selectedimaging mode. For example, the system is adapted to implement adual-energy image acquisition process for at least one image acquired in2D, 3D or a combination (combo) mode. In addition, the system ay beconfigured to perform a background subtraction image acquisition processfor images acquired in dual-energy 2D, 3D and/or combo modes.

In addition to enabling the selection of various imaging processeswithin each image mode, the system may be configured to enable a user tocustomize the acquisition parameters of a given mode or process. Thusthe system may further allow the user to identify acquisition parameterssuch as contrast agent, kV, mA, image timing, and x-ray filter type. Aswill be described in more detail later herein, the selection ofparameters may be varied between different 2D image acquisitions, suchas between sequential projection images Tp during a tomosynthesisacquisition, and to trigger imaging in relation to the timing ofintroducing a contrast agent.

In addition to enabling selection of acquisition modes and operatingparameters, the user interface may allow selection of various forms ofimage processing that are to be used on the captured image, including a3D reconstruction process (backward projection, forward projection, withweighting, etc.), noise filtering algorithms, subtraction of differentenergy images with or without differential weighting, addition ofdifferent energy images with or without differential weighting, etc.Alternatively, the control module may be programmed to select apreferred method of image processing in accordance with a selectedacquisition mode, or in accordance with a selected operating parameter,or a combination thereof.

These and other features will now be described in greater detail withregard to the figures.

Image Acquisition

One example is an x-ray image acquisition system that is optimized formammography and breast tomosynthesis and is further modified fordual-energy imaging and for the use of a contrast agent. One system thatcan serve as a basis for further modifications is the Selenia®Dimensions® tomosynthesis imaging system, manufactured and sold byHologic, Inc., of Bedford Mass. This system is a combo-mode systemcapable of acquiring images in either or both 2D and 3D mode, but itshould be clear that this is not the only example of a suitable system,that tomosynthesis-only systems also may serve as a basis formodification, and that some aspects of mammography-only systems also maybe useful as a basis for further modifications. Accordingly, the systemsand methods described in this patent specification are not limited to aparticular starting system that can be used or modified to carry out therequired processes. Certain aspects of examples of a starting system aredescribed in the commonly owned patents cited above.

FIGS. 1-3 illustrate various components of a non-limiting example of amulti-mode mammography/tomosynthesis system that can carry out theprocesses described in this patent specification with suitable additionsor modification for dual-energy imaging described below. The systemcomprises a gantry 100 and a data acquisition work-station 102. Gantry100 includes a housing 104 supporting a tube arm assembly 106 rotatablymounted thereon to pivot about a horizontal axis 402 and carrying anx-ray tube assembly 108. X-ray tube assembly 108 includes (1) an x-raytube generating x-ray energy in a selected range, such as 20-50 kV, atmAs such as in the range 3-400 mAs, with focal spots such as a nominalsize 0.3 mm large spot and nominal size 0.1 mm small spot (2) supportsfor multiple x-ray filters such as molybdenum, rhodium, aluminum,copper, cesium iodide, silver and tin filters, and (3) an adjustablecollimation assembly selectively collimating the x-ray beam from thefocal spot in a range such as from a 7 by 8 cm rectangle to a 24 by 29cm rectangle when measured at the image plane of an x-ray image receptor502 included in the system, at a maximum source-image distance such as75 cm. Also mounted on housing 104, for rotation about the same axis 402(or a different axis), is a compression arm assembly 110 that comprisesa compression plate or paddle 122 and a receptor housing 114 having anupper surface 116 serving as a breast plate or platform and enclosing animage detector subsystem system 117 comprising a flat panel x-rayimaging receptor 502 (FIG. 2 ), a retractable anti-scatter grid, and amechanism for driving and retracting anti-scatter grid between aposition in which the imaging x-ray beam passes through the grid and aposition in which the grid is outside the imaging x-ray beam. Housing104 also encloses a vertical travel assembly 404 for moving tube armassembly 106 and compression arm assembly 110 up and down to accommodatea particular patient or imaging position, a tube arm assembly rotationmechanism to rotate tube arm assembly 106 about the horizontal axis fordifferent imaging positions, a detector subsystem rotation mechanism forrotating components of detector subsystem 117 about the horizontal axisto accommodate different operations modes, and a couple/uncouplemechanism to selectively couple or uncouple tube arm assembly 106 andcompression arm assembly 110 to and from each other, and tube armassembly 106 and detector subsystem 117 to and from each other. Housing104 also encloses suitable motors and electrical and mechanicalcomponents and connections to implement the functions discussed here. Apatient shield 200, schematically illustrated in FIG. 2 , can be securedto compression arm assembly 110 to provide a mechanical interlockagainst patient contact with the rotating x-ray tube arm assembly 106.Work-station 102 comprises components similar to those in the Selenia®mammography system and in the Selenia® Dimension combo system, includinga display screen (typically a flat panel display that may includetouch-screen functionality), user interface devices such as a keyboard,possibly a touch-screen, and a mouse or trackball, and various switchesand indicator lights and/or displays. Work-station 102 also includescomputer facilities similar to those of the Selenia® the Selenia®Dimensions® system (but adapted through hardware, firmware and softwaredifferences) for controlling gantry 100 and for processing, storing anddisplaying data received from gantry 100. A power generation facilityfor x-ray tube assembly 108 may be included in housing 104 or inwork-station 102. A power source 118 powers work-station 102. Gantry 100and work-station 102 exchange data and controls over a schematicallyillustrated connection 120.

As illustrated in FIG. 3 , additional storage facilities 602 can beconnected to work-station 102, such as one or more optical disc drivesfor storing information such as images and/or for providing informationto work-station 102 such as previously obtained images and software, ora local printer (not shown). In addition, the disclosed system can beconnected to a hospital or local area or other network 604, and throughthe network to other systems such as a soft copy workstation 606, a CAD(Computer Aided Detection) station 608 for computer-processingmammography and/or tomosynthesis images to identify likelyabnormalities, an image printer 610 for printing images, a technologistworkstation 612, other imaging systems 614 such as other mammographysystems or systems for other modalities for exchange of images and/orother information, and to a PACS (Picture Archiving) systems 616 forarchiving images and other information and/or retrieving images andother information.

In standard mammography mode, typically used for screening mammography,tube arm assembly 106 and compression arm assembly 110 are coupled andlocked together in a relative position such as seen in FIG. 1 , suchthat an x-ray beam from x-ray tube assembly 108 illuminates x-rayreceptor 502 when the patient's breast is compressed by compressiondevice 112. In this mode, the system operates in a manner similar tosaid Selenia® system to take a mammogram. Vertical travel assembly 404and tube arm rotation mechanism can make vertical adjustments toaccommodate a patient, and can rotate tube arm assembly 106 andcompression arm assembly 110 together as a unit about the horizontalaxis for different image orientations such as for CC and for MLO images.For example, tube arm assembly 106 and compression arm assembly 110 canrotate between (−195.degree.) and (+150.degree.) about the axis. As inthe Selenia® system, compression device 112 includes a compressionpaddle 122 that can move laterally, in a direction along the chest wallof a patient, to adjust for different imaging orientations. Thecompression paddle may comprise any one of a plurality of types ofpaddles, including but not limited to a full paddle, a spot paddle, or acurved paddle (which may be preferred for use in contrast imageacquisition processes described below), and may be configured to tiltagainst a spring bias and/or to move laterally, as described in thecommonly owned patents identified above.

In tomosynthesis mode, as used for example in said Selenia® Dimensions®system and as described in said U.S. Pat. No. 7,869,563, tube armassembly 106 and compression arm assembly 110 are decoupled such thatcompression arm assembly 110 stays in one position, compressing thepatient's breast, while tube arm assembly 106 rotates about thehorizontal axis, for example +/−15 degrees relative to compression armassembly 110. Tomosynthesis can be carried out for different imageorientations, so that compression arm assembly 110 can be rotated aboutthe horizontal axis (alone or together with assembly 106) for a desiredimage orientation and locked in place, and then tube arm assembly 106can be rotated relative to that position of compression arm assembly 110for tomosynthesis imaging over +/−15 degree or some other desiredangular range. For example, low dose tomosynthesis may be performed overa seven degree angular range to collect in the area of seven projectionimages.

In a combination mode, during a single compression of the patient'sbreast the system takes a conventional mammogram and tomosynthesisimages. In this mode, while the breast remains compressed in compressionarm assembly 110, (1) tube arm assembly 106 sweeps and x-ray receptor502 rocks, each through an appropriate angle, and x-ray exposures aretaken for tomosynthesis images, and (2) a standard mammogram is taken.The standard mammogram can be taken at a 0 (zero) degree angle relativeangle between tube arm assembly 106 and a normal to the imaging plane ofx-ray receptor 502, and can be taken before or after the tomosynthesisimages are taken or between the taking of two successive tomosynthesisimages. Typically, each tomosynthesis image utilizes substantially lowerx-ray dose than the standard mammogram.

For example, as described above, the total dosage of all projectionimages taken during the tomosynthesis scan can range from 0.25 to 2.0times that of the dose of a single mammogram. The relationship betweenthe two dosages can be user-selected to control any one of the x-raytube voltage, current, tomosynthesis scan angle, number of projectionimages obtained, etc. In alternate embodiments, the dosage may bealtered via a simple switch on the gantry, or through a user control ata radiologist workstation. In still alternate embodiments the dosage mayvary automatically as the radiologist switches between modes.

Image Acquisition Process Selection

One important characteristic of any digital imaging system is theability to vary the amount and intensity of radiation used to generateany image. Radiation intensity is related to the atomic number (Z) ofthe x-ray target, the x-ray current (mA), x-ray voltage and x-ray beamfiltration. Radiation intensity is varied to improve image quality,which in turn can improve diagnostic sensitivity. When radiationintensity increases, quantum mottle (image noise caused by photonabsorption) tends to decrease and vice versa.

Many mammography and tomosynthesis systems allow the operator to controlx-ray exposure by manually setting technique factors such as mA andmSec. Some systems include an Automatic Exposure Control (AEC)functionality which controls a duration of administration of radiation,turning off the x-ray source when the desired dose has beenadministered. Automatic Exposure Control (AEC) methods may vary thedosing parameters, including exposure time, kV, mA and filter modes foran image to vary the exposure and the radiation intensity.

While such control over acquisition parameters may provide someimprovement over image quality, according to one aspect of the systemand method described in this patent specification, improved imagequality may be provided by incorporating additional acquisitionprocesses into 2D, 3D or combo systems to realize the benefits ofcontrast image enhancement according to new approaches described in thispatent specification.

A breast imaging system according to examples described in this patentspecification combines the capabilities of combined 2D and/or 3D breastx-ray imaging with benefits from contrast image acquisition processes.Biopsy capability (stereotactic or tomosynthesis guided) may also beintegrated into the system, with lesion localization software utilizingany images selected from a group including simple 2D images, 3Dprojection images, 3D reconstructed data, or any of the 2D, 3Dprojection and 3D reconstructed data obtained during a dual energy orbackground subtraction image acquisition process.

With such arrangements, the following image protocols are supported:

-   -   Contrast imaging (background subtraction) using a single high or        low energy image acquisition technique, in 2D or 3D mode.    -   Dual-energy contrast imaging in 2D or 3D mode;    -   Dual-energy contrast imaging in 3D mode, wherein high and low        energy exposures occur at different angles during a        tomosynthesis scan; [high and low energies can be reconstructed        separately and combined to form the dual energy volume];    -   Dual-energy imaging in a combo system that acquires dual-energy        2D and dual-energy 3D images;    -   In combo imaging mode, where the 2D image data set is acquired        using a single energy, and the 3D image data set is acquired        using dual-energy imaging;    -   In combo imaging mode, where the 2D image data set is acquired        using dual-energy imaging, and the 3D image data set is acquired        using a single energy image;    -   Tomosynthesis imaging mode, wherein among a total of N views in        a contrast tomo scan wherein the breast remains n compression        throughout the scan, different projection images are allotted        different dose, kVps, mAs and filters for greater flexibility of        different applications;    -   Tomosynthesis mode wherein a low energy scans and high energy        scans alternate in a series f acquired projection images;    -   Tomosynthesis mode wherein low energy and high energy scans are        performed for the projection images, in unequal ratios in user        selectable patterns;    -   Stereotactic biopsy using contrast agent, and either dual energy        or background subtraction imaging;    -   Upright biopsy using tomosynthesis scan images obtained using a        contrast agent and either dual-energy or background subtraction        imaging;

Other variations of combinations of contrast imaging and imageacquisition modes are within the scope of this patent specification.

Image Acquisition Parameter Selection

Once an image acquisition mode and an acquisition process areidentified, acquisition parameters and image processing techniques canbe varied at a projection image granularity by varying at least one ofkV, mA and/or filter for each 2D image capture.

Several modifications to existing mammography and/or tomosynthesisbreast imaging systems may be made to support contrast imaging. Forexample, within the x-ray source, mechanisms that allow fast switchingbetween kV, mA and x-ray beam filters may be provided to supportdual-energy imaging between and within image capture modes. For example,an x-ray filter wheel may be provided to switch filters between low andhigh energy pulses. A variety of different filters, such as rhodium,silver, aluminum, copper and cesium iodide may be provided to providethe desired energy for different contrast agents.

FIG. 3 a schematically illustrates an example where a focal spot 108 ainside x-ray source 108 emits an imaging x-ray beam 108 b toward animaging x-ray receptor. The beam passes through a variable filterassembly 108 c that contains a mechanism for interposing a selectedfilter in the beam path to thereby control the energy range of thex-rays that continue toward the imaging receptor. A filter changecontrol 108 d determines which filter will intercept the x-ray beam, andin turn is controlled by system settings or by a user through unit 102.Variable filter arrangement are known in the field, as they are used ina variety of systems, including dual energy bone densitometry systems ofthe type offered by the common assignee. A variable collimator 108 econtrols the area of the x-ray imaging beam at the imaging plane of thereceptor, and is in turn controlled by a collimator controller 108 fthat can also receive commands from unit 102.

The new systems described in this patent specification allow users toselect physical acquisition parameters at a projection imagegranularity. For example, FIG. 4 illustrates an example of process stepsthat can be followed. In step 400 a decision is made whether to set thesystem to operate in a contrast-enhanced mode and in step 402 a decisionis made whether to operate the system in a dual-energy mode. Thesedecisions can be made by a user, or can be made automatically by thesystem depending on some information that a user enters. In step 404 theuser or the system selects whether to operate in 2D mode only, in 3Dmode only, or in a combination of 2D and 3D modes. In step 406, thesystem or the user may customize acquisition parameters such as kV, mAs,etc., and in step 408 the system operates with the settings selected insteps 400-406 to acquire images Tp and/or Mp.

FIG. 5 illustrates an example of a tomosynthesis projection imagecustomization table that may be presented to the user for manualcustomization of images of a tomosynthesis scan. Although certain fieldsare shown in the table, this patent specification anticipates that anyacquisition variable may be made available to a user for customizationof the image in this manner. Such a table may initially be populatedwith default values, which may be system defaults or default valuespopulated following analysis of image data received in response to AEC,or may be filled in by a user and entered into the system.

Image Processing Selection

The new system also allows different image processing to be performed onreceived images, where the image processing techniques may be determinedin response to a type of acquisition (i.e., a tomosynthesis acquisition,a 2D acquisition, a dual-energy acquisition, a contrast acquisition).Thus, for example, images acquired using high energy may be processedusing different algorithms than images acquired using low energy. Theimage processing technique may be preprogrammed based on the selectedacquisition mode or alternatively may be selected in response to userinput. For the purposes of this patent specification, image processingrefers to any manipulation and combination of the images, includingnoise filtering and image reconstruction. Some of the processing may bea function of the acquisition mode. For example, when performingbackground subtraction contrast imaging using tomosynthesis images, preand post injection projection images may be subtracted, and theresulting signal shifted to register the images to compensate forpatient motion.

In one embodiment, the new system enables the utilization of either gaincontrolled images or air-map corrected images as a basis for thecontrast image processes (i.e., the images may be processed prior to thesubtraction or addition processes). Gain controlled images are imagesthat have been processed to compensate for system gain to increase SNR,for example using techniques described in said commonly assigned U.S.Pat. No. 7,991,106.

Display

A display of the new system may be used to display images captured usingany of the modalities (2D, 3D, combo), using any image acquisitionprocess. The display includes the ability to display the images in avariety of configurations, including singularly, side by side, toggled,or in cine-mode. With such an arrangement, a health professional maysimultaneously view (or toggle between, or view in cine), the 2D image,3D projection image or 3D slice image of a breast, at either the lowenergy acquisition, high energy acquisition, or following subtraction ofthe two, with or without the use of contrast agents, thereby enhancingthe ability to visualize and characterize lesions.

FIG. 6 a illustrates an example in which different types of images arepresented side-by-side, in respective windows of a computer display 102a. FIG. 6 b schematically illustrates an example of computer display 102a that concurrently shows six different images of a patient's breast: asingle-energy tomosynthesis projection image TpSE, a single-energyreconstructed tomosynthesis slice image TrSE, a single-energy mammogramMpSE, a dual-energy tomosynthesis projection image TpDE, a dual-energyreconstructed tomosynthesis slice image TrDE, and a dual-energymammogram MpDE, It should be understood that in this context the termsingle-energy refers to the range of energies that an x-ray tube emitsat a particular parameter setting of parameters that determine x-ray theenergies that the tube emits, and the term dual energy refers to twosuch energy ranges that may partly overlap. It should also be understoodthat FIG. 6 b illustrates one of the many examples of arranging imagesaccording to this patent specification, and that the image display mayshow only a subset of the illustrated images, may show images in adifferent relative arrangement, may show multiple images of the samekind (e.g., multiple images Tp, etc.), may show superimposed images,and/or may show images in cine mode, and may show a single image overthe entire screen or may divide the screen into a different number ofwindows.

FIG. 7 illustrates a scope of imaging in different modes of operation,of a combo system that operates in either or both of a 2D imagingmammography mode and a 3D imaging tomosynthesis mode. In each of these2D and 3D modes, the system can operate image the breast with or withoutcontrast agent in the breast. In either or both of the 2D and 3D modes,and with or without contrast agent in the breast, the system can carryout dual-energy imaging or background subtraction imaging. As seen inFIG. 7 , these capabilities allow for many different combinations ofmodes such as 2D using single-energy (SE) and contrast enhancement (CE),2D using SE, 3D using CE, 3D using DE, etc. FIG. 8 illustrates a scopeof imaging when using a 2D only system, i.e., a system that does notinclude 3D tomosynthesis capabilities. In the FIG. 8 example, the systemcan be used in single-energy or dual-energy modes, in each case with orwithout contrast agent in the breast. FIG. 9 illustrates the operationof a 3D only system that can operate in 3D imaging mode usingsingle-energy or dual-energy imaging, in either case with or withoutcontrast agent in the breast.

Although the above has described the use of the new system with regardto acquisition of both tomosynthesis and mammogram images, this patentspecification is not limited to an integrated multi-mode system butapplies to any system that is capable of performing tomosynthesis. Forexample the new system may include only tomosynthesis imagingcapability. Such systems may use a legacy mammogram for example forcalcification detection, or may obtain a single tomosynthesis image athigher dosage to use as their 2D image, or may synthesize a mammogramimage from tomosynthesis projection images. In addition, the new systemmay incorporate tomosynthesis imaging capability with a differentmodality, such as molecular breast imaging or ultrasound imaging. Inshort any breast imaging systems which includes tomosynthesis imagingcapabilities falls within the scope of this patent specification. Stillin addition, some of the improvements described in this patentspecification also apply to systems that take only 2D images.

The above specific examples and embodiments are illustrative, and manyvariations can be introduced on these examples and embodiments withoutdeparting from the spirit of the disclosure or from the scope of theappended claims. For example, elements and/or features of differentillustrative embodiments may be combined with each other and/orsubstituted for each other within the scope of this disclosure andappended claims.

PREFERRED EXAMPLES

In a preferred example, the system described in this patentspecification obtains (i) 3D tomosynthesis slice images TrSE of apatient's breast that represent respective slices of the breast and arereconstructed through computer-processing of a multiplicity ofsingle-energy x-ray 2D tomosynthesis projection images TpSE of thepatient's breast, (ii) a low-energy x-ray 2D mammogram MpL, and (ii) ahigh-energy x-ray 2D mammogram MpH of the breast. The Tp, MpL and MpHimages preferably are taken in a single breast compression, while thebreast remains immobilized. The system computer-processes the 2Dlow-energy mammogram MpL and the 2D high-energy mammogram MpH to form aweighted combination dual-energy 2D mammogram image MpCDE that tends tohighlight vascularity in the breast. The system displays, preferablyconcurrently, (i) the combination 2D image MpCDE, which can help revealspositions of possible vascular abnormalities in two dimensions, and (ii)3D slice images TrSE in which the abnormalities appear and which canhelp reveal 3D positions of the abnormalities and the appearance of theabnormalities in the slice images.

Preferably, the system is configured respond to an identification of anabnormality in the MpCDE image to automatically identify the subset ofTrSE images in which the abnormality appears. Also preferably, thesystem is configured to concurrently display the MpCDE image and eitherone or more but not all of the images of said subset of TrSE images, orthe entire subset.

FIG. 10 illustrates steps of a method for carrying out imaging accordingto the preferred example. In step 1000, imaging parameters such as thoseillustrated in FIG. 4 are set for an imaging sequence. This can be doneeither by storing a default in the system, e.g., in acquisitionworkstation 102 shown in FIG. 1 , or more typically by selectingparameters adapted to a particular patient and/or a particular study,using for example a table such as illustrated in FIG. 5 . In step 1001,a contrast agent is injected, such as a standard FDA-approved lowosmolarity Iodine contrast agent. In one example, 350-370 mg/ml of thecontrast agent are injected at a rate of 3 to 3.5 ml/sec, or withinsafety parameters of the IV gauge in place, with a total volume of 1.5ml/kg patient weight up to a maximum of 150 ml. In general, the agentcan be the same as commonly used clinically for contrast-enhanced CTscanning of the chest and abdomen. The injection can be in theantecubital or forearm vein. Step 1002 is waiting time, typically of theorder of a minute or two after the start of the injection. The durationof step 1002 is set based on health professionals' assessment of thetime needed for the contrast agent to reach a desirable concentration inthe breast. In step 1004, the patient's breast is compressed in themanner known for tomosynthesis images and a system such as thatillustrated in FIG. 1 , or such as the Selenia® Dimensions® availablefrom the assignee, operates in a single-energy tomosynthesis mode totake plural single-energy projection images TpSE of the breast, forexample 22 images TpSE, each from a respective different angle of theimaging x-ray beam relative to the breast, over an angular range such as±15°. In step 1006 and while the patient's breast remains compressed andimmobilized, the system takes a low-energy mammogram MpL and ahigh-energy mammogram MpH, for example by returning the x-ray source toa 0° position and taking the image MpL with one x-ray filter in theimaging x-ray beam, then changing to a different x-ray filter and takingthe image MpH. Preferably, x-ray energies in the 30-40 kVp range areused for the TrSE images, less than 35 kVp (e.g., in the 28-30 kVprange) for the MpL image, and more than 45 kVp (e.g., in the 45-49 kVprange) for the MpH image. However, different energies can be used in amanner consistent with clinical practice. As one example, a Rhodium orSilver x-ray filter can be used for the MpL image but a Copper filterfor the MpH image. The other imaging parameters follow typical clinicalpractice and may depend on factors such as the thickness and x-raydensity of the compressed breast.

In step 1008, the TpSE images are computer-processed to form TrSEimages, using reconstruction algorithms of the type described in thematerial incorporated by reference, and the MpL and MpH images arecomputer-processed to form a combined image MpCDE. For example, thecombined image is obtained according to the relationship MpCDE=MpH−kMpL,where k is a weighting factor and typically k>1, as is known in thedual-energy x-ray imaging technology. In step 1010, a display protocolis selected, either automatically according to a preset default protocolor as selected by a user for a particular patient study or a particulardisplay, and can be set into a workstation such as unit 102 of FIG. 1 orinto a separate imaging workstation. In step 1012 one or more of theimages TrSE and MpCDE are displayed on a screen such as screen 102 ashown in FIG. 6 b . In addition, other images can be displayed on thesame screen or other screens, such as any of the images TpSE and otherimages such as images of the breast obtained at other times with thesame or different modalities such as, without limitation, MRI, CT,nuclear medicine imaging devices, and ultrasound

Numerous variations are possible in the order of steps illustrated inFIG. 10 . For example, the order of steps 1004 and 1006 can be reversed.Step 108 can start before step 1006, or well after step 1006. Steps1008, 1010 and 1012 can be carried out in devices remote from unit 100illustrated in FIG. 1 .

It should be appreciated that the preferred example illustrated above isonly one of many examples consistent with this patent specification, andthat other combination of modes and steps also are within the scope ofthe specification

1. (canceled)
 2. A method for imaging a breast of a patient, the methodcomprising: injecting a contrast agent into the patient; immobilizing,between an x-ray source and an x-ray detector of an imaging system, thebreast of the patient; performing a 2D imaging procedure on the breastof the patient, the 2D imaging procedure being based on dual energyexposures; generating at least one image that visualizes the contrastagent; and processing the at least one image to identify one or morelesions, wherein the one or more lesions are identified by quantifyingbrightness of breast tissue under contrast.
 3. The method of claim 2,further comprising displaying the at least one image on the imagingsystem.
 4. The method of claim 2, wherein quantifying the brightness ofbreast tissue under contrast includes characterizing vascularity ofbreast tissue under contrast.
 5. The method of claim 4, wherein thevascularity of breast tissue under contrast is indicative of a presenceof angiogenesis with the breast tissue.
 6. The method of claim 2,wherein the at least one image includes a dual energy subtraction image.7. The method of claim 2, wherein the 2D imaging procedure is acraniocaudal (CC) or a mediolateral oblique (MLO) orientation.
 8. Themethod of claim 2, wherein the contrast agent is iodine-based.
 9. Themethod of claim 2, wherein the dual energy exposures occur at energiesabove and below a k-edge of iodine.
 10. The method of claim 2, whereinthe x-ray source includes at least two filters, and wherein the 2Dimaging procedure includes changing between a first filter and a secondfilter between the dual energy exposures.
 11. The method of claim 2,wherein injecting the contrast agent into the patient occurs at leastone minute prior to immobilizing the breast of the patient.
 12. Themethod of claim 2, further comprising performing a 3D imaging procedureon the breast of the patient.
 13. A imaging system for imaging a breastof a patient, the system comprising: an x-ray source; an x-ray detector;a compression mechanism disposed between the x-ray source and the x-raydetector; and a control module programmed with a set of instructionsthat when executed cause the imaging system to perform a set ofoperations, comprising: immobilizing, via the compression mechanism, thebreast of the patient having a contrast agent; performing a 2D imagingprocedure on the breast of the patient, the 2D imaging procedure beingbased on dual energy exposures; generating at least one image thatvisualizes the contrast agent; and processing the at least one image toidentify one or more lesions, wherein the one or more lesions areidentified by quantifying brightness of breast tissue under contrast.14. The imaging system of claim 13, further comprising a display fordisplaying the at least one image on the imaging system.
 15. The imagingsystem of claim 13, wherein within the set of operations, quantifyingthe brightness of breast tissue under contrast includes characterizingvascularity of breast tissue under contrast.
 16. The imaging system ofclaim 15, wherein within the set of operations, the vascularity ofbreast tissue under contrast is indicative of a presence of angiogenesiswith the breast tissue.
 17. The imaging system of claim 13, wherein theat least one image includes a dual energy subtraction image.
 18. Theimaging system of claim 13, wherein the 2D imaging procedure is acraniocaudal (CC) or a mediolateral oblique (MLO) orientation for atleast the x-ray source.
 19. The imaging system of claim 13, wherein thecontrast agent is iodine-based.
 20. The imaging system of claim 13,wherein the dual energy exposures occur at energies above and below ak-edge of iodine.
 21. The imaging system of claim 13, wherein the x-raysource includes at least two filters that are changed between during thedual energy exposures of the 2D imaging procedure.